This invention relates to an improved, internal combustion, reciprocating engine. The engine employs thermal regeneration to improve its efficiency and power. Regeneration is accomplished through the use of an alternating flow heat exchanger, hereafter referred to as the regenerator and sometimes called a recuperator. The engine consists of one or more cylinders containing a pair of opposed pistons separated by a stationary regenerator. The pistons are suitably connected to one or more power output shafts. The volume on one side of the regenerator, i.e., between the regenerator and one of the pistons, is referred to as the hot volume. The volume between the regenerator and the other piston is referred to as the cold volume. The engine is equipped with a means to introduce gaseous or liquid fuel into said hot volume. Means are also provided to introduce fresh working fluid and to remove exhaust gases from the cold volume. This engine performs a thermodynamic cycle approximated by a regenerated Otto or diesel cycle. It can provide greater expansion than compression, and other operating features that are unique, and provides critical and substantial improvements over previous engines.
Thermal regeneration is the capturing of thermal energy from a thermodynamic cycle (or a heat engine operating on some thermodynamic cycle) and the utilization of that energy within the cycle or engine to improve the cycle or engine""s performance. This is commonly done with many heat engines, including Stirling engines, gas turbines, and Rankine cycle devices. In a gas turbine, consisting of a compressor, combustor, and turbine, the temperature of the air leaving the turbine is often greater than the temperature of the air leaving the compressor. If the energy in the turbines exhaust can be transferred to the air leaving the compressor, it will not be necessary to add as much heat (fuel) in the combustor to raise the air temperature to the desired turbine inlet temperature. This means that the same work is accomplished, but less fuel is employed. Therefore, the specific fuel consumption of such a thermally regenerated gas turbine is improved. Thermal regeneration of gas turbines is commonly accomplished by the use of alternating flow heat exchangers that transfer energy from the exhaust gases to the compressed air.
In principle, any internal combustion engine can be thermally regenerated. This can be done by transferring heat from the gases at the conclusion of the expansion stroke to the gases of the next cycle at the conclusion of the compression stroke. The benefits that can be attained thereby are substantial. Fuel consumption is reduced in a manner similar to that of the regenerated gas turbine.
In addition, a regenerated internal combustion engine is thermodynamically capable of providing higher gas temperatures, which results in even greater improvements in efficiency and power. Since reciprocating engines only experience these higher temperatures for brief times, they can withstand these higher temperatures to some extent. Thus the benefits of regeneration are even greater for an internal combustion engine than they are for the temperature limited gas turbine. The advantages of thermally regenerated gasoline or diesel engines are readily apparent and quite substantial. Unfortunately, viable and effective means by which this can be accomplished have not previously been disclosed or developed.
Like the regenerated gas turbine the regenerative heat transfer in an internal combustion engine, such as a reciprocating engine, can best be accomplished through the use of an alternating flow heat exchanger. This approach is commonly applied in the externally combusted Stirling engines and has been proposed in a variety of forms for regenerated, internal combustion, reciprocating engines. There are two basic approaches: (1) force the working fluid to pass through a stationary regenerator, or (2) move the regenerator through the gas.
Many inventors in this field have taken the former approachxe2x80x94i.e., a stationary regenerator. This has led to a number of approaches such as those found in U.S. Pat. No. 155,087 to Hirsch, U.S. Pat. No. 2,239,922 to Martinka, U.S. Pat. No. 3,777,718 to Pattas, U.S. Pat. No. 3,871,179 to Bland, U.S. Pat. No. 3,923,011 to Pfefferle, U.S. Pat. No. 4,004,421 to Cowans, U.S. Pat. No. 4,074,533 to Stockton, U.S. Pat. No. 4,630,447 to Webber, SAE paper 930063, by Ruiz, 1993, and Carmichael (Chrjapin Master""s thesis, MIT, 1975). All of these approaches involve at least two cylinders, generally one in which compression occurs and a second where the combustion and expansion occur. In the flow passage connecting these cylinders, or in one of the cylinders, there is a stationary permeable material that comprises the regenerator. The regenerator is the alternating flow heat exchanger. The expanded combustion gases are passed through the regenerator and transfer thermal energy to it. During the next cycle compressed air is forced through the regenerator thereby absorbing this energy. Thus heat is transferred from the hot exhaust gases to the compressed airxe2x80x94the essence of thermal regeneration.
Unfortunately, none of these earlier approaches for utilizing a stationary regenerator to accomplish a regenerated, internal combustion reciprocating engine have been successful. This is due to a number of causes which were not apparent to the previous inventors, including, the poorer computing capabilities generally available to them, the extensive time required to properly analyze such engines, or both. We have developed detailed computer models of regenerated engines that provide new insight into the processes occurring and which validate the improved regenerated engine disclosed herein.
The primary difficulty with these earlier stationary regenerator engine designs is that they do not have the capability to move the gas through the regenerator at the appropriate times during the cycle. This can be critically important and make all the difference between an engine that will barely run and one that has high fuel economy and power density. One of the primary, novel features of this invention is that it recognizes and specifies near optimum motion of the pistons. It also provides a means by which such motion can be accomplished.
In one of the most promising of the early regenerated engine designs, a single cylinder is divided into two sections by a stationary regenerator. The regenerator is a porous, high temperature material in the shape of a disc having a diameter equal to the cylinder bore. The cylinder ends are closed by pistons which are connected by drive mechanisms to the power output shaft. The volume between one piston and the regenerator is referred to as the cold volume and has adjacent means for the exchange of working fluid within that cold volume. The volume between the regenerator and the other volume is referred to as the hot volume and has adjacent means to inject fuel into the hot volume. The piston in the hot volume is referred to as the hot piston and the piston in the cold volume is referred to as the cold piston.
In stationary regenerator engines, the working fluid is forced through the regenerator by the actions of the pistons. Engine performance is very highly dependent upon the exact schedule of the pistons"" motions. None of the previous inventors of regenerated engines has proposed a mechanism that could provide the required piston motions. Also, none of the previous inventors has specified the required piston motions in sufficient detail to allow an appropriate drive mechanism to be selected or developed. U.S. Pat. No. 3,777,718 to Pattas, for example, discloses a conventional crank and eccentric arrangement as a piston drive mechanism for controlling piston positions in the engine. It is not possible for such a mechanism to provide the very unusual and non-sinusoidal type of motion required by the regenerated cycle. A far more flexible design approach is required for the piston drive mechanism, as will be discussed hereinbelow.
One such exemplary embodiment for controlling the piston motion is an engine having a barrel cam, alternatively known as an axial cam or a cylindrical cam. An opposed piston cam engine that is useful for this purpose is disclosed in U.S. Pat. No. 5,375,567 to Lowi, which is incorporated by reference in its entirety as if disclosed herein.
In addition to being unable to provide or specify satisfactory piston motion, many of the earlier designs specified incorrect or poorer performing motions for the pistons. For example, Pattas proposes that after the hot gases have expanded on the hot side, the hot piston should be moved so that the hot gases are forced back through the regenerator. Then, xe2x80x9cas the working medium builds up in the cylinder of the cold gas section, the cold piston is moved outward from the regenerator to expand the cold gas sectionxe2x80x9d. Our analyses clearly show that this type of motion results in very poor performance. It is much more advantageous to fully expand the gas by moving the cold piston to a position near to its full outward position and to xe2x80x9cblow downxe2x80x9d the cylinder prior to the hot piston""s inward stroke. The engine disclosed herein avoids this failure by providing near optimum motions of the pistons and by providing a piston drive mechanism that can accomplish these motions.
Finally, the engine disclosed herein has an inherent ability to provide greater expansion than compression, a process sometimes referred to as a xe2x80x9cMiller Cycle,xe2x80x9d more generally known as the more-complete-expansion cycle. This feature can dramatically improve fuel efficiency and power.
This invention is an internal combustion, reciprocating, regenerated engine made up of a number of similar working units, often referred to as cylinders. Each working unit is comprised of a cylinder that is closed at each end by a movable piston that is connected to a power output shaft. Means are provided to permit and control the flow of working fluid into and out of the cylinder and to inject fuel into the cylinder. An alternating flow heat exchanger, called a regenerator, is located within the cylinder, between the pistons. The pistons are moved in such a manner, and other means are provided, so that the following processes will occur: (1) compression of the working fluid, (2) regenerative heating of the working fluid, (3) combustion within the heated working fluid, (4) expansion of the working fluid, (5) regenerative cooling of the working fluid, and (6) exchange of a portion of the working fluid. These processes occur in sequential fashion, with some degree of overlap. The primary and most unique feature of this invention is that these processes occur in the appropriate manner and timing so as to provide optimum power and fuel efficiency.
One embodiment of this invention utilizes a barrel cam as a means by which the pistons can be moved in the unusual manner required by the thermodynamic cycle of this engine.
The primary object of this invention is to provide a highly efficient, regenerated, internal combustion engine.
Another object of this invention is to provide an engine with very high brake mean effective pressure.
Another object of this invention is to exploit the high payoff to be obtained from regenerating an Otto or diesel cycle engine.
Another object of this invention is to exploit the high degree of freedom in piston motion that is attainable with a barrel cam, thereby providing the highly unconventional piston motion required by the regenerated engine.
Another object of this invention is to provide a regenerated engine employing a stationary regenerator in which the pistons"" motions are designed to provide good performance.
Other objects, advantages, and novel features will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.